Research on the normal emissivity of graphite between 150 and 500 °C by an infrared camera for nuclear fusion devices

Abstract

• An emissivity measurement equipment by using an infrared camera is constructed and calibrated by a blackbody furnace with a suitable emissivity model. • By using an infrared camera with no filter (band wavelength range of 7.5 μm–13 μm), a 10.2 ± 0.1 μm filter, and a 10.8 ± 0.19 μm filter, the relationship between the temperature and emissivity of graphite and the residual between data and model are obtained respectively and compared. • The emissivity of graphite at different roughness is studied, and uncertainty quantification is used to provide an error estimate for the resulting curves. Due to the advantages of high-temperature resistance, low thermal expansion coefficient, and thermal shock resistance, etc., graphite is regarded as one of the materials for the first wall of nuclear fusion devices. The real-time monitoring of temperature distribution of the first wall based on an infrared camera is widely used to guarantee the stable operation of devices. To accurately measure the temperature of the first wall, it is important to measure the normal emissivity of graphite. However, the emissivity of graphite is affected by many factors. For example, the effect of the surface layers, like carbon-hydro layers-layers, will influence the measurement of the emissivity. The ambition of this work is to study the relationship between graphite emissivity and infrared camera with filters of different wavelengths and the roughness of graphite, and then give the proposed emissivity model to improve the accuracy of graphite surface temperature measurement. The experiment is carried out with a FLIR infrared camera and calibrated by using a blackbody furnace. The emissivity at given temperatures is systematically investigated. By using an infrared camera with no filter (band wavelength range of 7.5–13 μm), a 10.2 ± 0.1 μm filter, and a 10.8 ± 0.19 μm filter, this paper studies the relationship between the temperature and emissivity of graphite from 150 °C to 500 °C and calculates the relative error of temperature measurement respectively. A suitable fitting model which fits emissivity curves is selected. The measurement results show the use of a 10.2 μm filter to measure the graphite surface temperature has the smallest relative error, the range is 0.90%∼1.17%. The emissivity of graphite with different roughness is also studied. At the same temperature, the greater the roughness of the graphite surface, the higher the emissivity value. The uncertainty of the emissivity measurement is analyzed, and its value is 0.0099–0.0211. The graphite surface temperature measurement method based on the emissivity model proposed in this paper provides useful references for the non-contact temperature measurement of the first wall in nuclear fusion devices. The research results can be used as a reference for plasma experiments in some fusion devices and other similar applications.